The ball bearing as a means of reducing friction between rotating or moving parts has enjoyed wide usage in a variety of different types of apparatus. However, in gyroscopic applications, the use of ball bearings constitutes an undesirable source of error torque, which results in unpermissible gyroscopic drift, noisy operation and a limited life (in the order of 5000 hours). In order to overcome the disadvantages of ball bearings, gas bearings have sometimes been used in gyroscopic applications. However, they have the principal disadvantage in that they cannot be used in flexure-suspended free gyroscopes because of imcompatibility in working pressure. Gas bearings of the hydrodynamic type require a gas pressure of the order of one atmosphere, whereas the gyroscope itself requires pressure lower than 1/5 atmosphere in order to achieve low damping.
In order to improve gyroscopic performance, liquid bearings of the type disclosed in U.S. Pat. No. 3,778,123, filed in the name of Harvey S. Hendler et al. and assigned to the same assignee as the present invention, have been proposed. That invention describes a liquid bearing with seals.
It is necessary in liquid bearings to utilize liquids with low viscosity, in the order of 0.5 to 1 centistoke, in order to obtain low damping. Unfortunately, such liquids also exhibit relatively high vapor-pressures. The liquid has to be confined in the bearing by means of seals to avoid loss of lubricant. The amount of liquid in the bearing gap is extremely small, in the order of 200 mg. The seals also have to accommodate a change in volume as the temperature of the bearing changes. Minute leakages, in the order of a few nanograms liquid/hour, will eventually shorten the length of life of the bearing.